1. Field of the Invention
The present invention relates to a liquid crystal displaying apparatus and a fabrication method thereof.
2. Description of the Related Art
In recent years, to accomplish a high speed picture process and a high quality display picture of a liquid crystal displaying apparatus, an active matrix drive type color liquid crystal displaying apparatus has been widely used. In this color liquid crystal displaying apparatus, switching thin film transistors are disposed for individual display pixels.
Generally, in a liquid crystal displaying apparatus, two glass substrates having electrodes are sealed with an adhesive agent and a sealing agent. Liquid crystal material is filled in the space between the two glass substrates. To keep the distance between the two substrates constant, plastic beads, or the like, with equal particle diameters are dispersed as spacers between the substrates. In a color liquid crystal displaying apparatus, a color filter layer having a color layer equivalent to three primary colors (RGB) is disposed on one of the two glass substrates.
In the active matrix drive type color liquid crystal displaying apparatus, as shown in FIG. 6, a thin film transistor (TFT) 47 composed of amorphous silicon (a-Si) as a switching device is disposed on one glass substrate 46 corresponding to each of a plurality of pixel electrodes 48 arranged in a matrix shape. The thin film transistor 47 has a gate electrode, a drain electrode, and a source electrode. The gate electrode is connected to a scanning line. The drain electrode is connected to a signal line. The source electrode is connected to a pixel electrode 48. In such a manner, an array substrate is structured. On the array substrate, a protection film and an alignment film 49 are successively disposed. The alignment film 49 aligns the orientation of liquid crystal molecules.
The other substrate is an opposite substrate that is conventionally composed of a transparent glass substrate 41, a light shielding layer (black matrix) 42, a three-primary-color filter 43, a color filter protection film, a common transparent electrode 44, and an upper alignment film 45. The light shielding layer 42 is disposed on the transparent glass substrate 41. The light shielding layer 42 is composed of for example a Cr metal film.
The pair of substrates are oppositely disposed with a spacer 51 so that they are spaced with a predetermined distance. The substrates are adhered with seal agent applied on the periphery thereof.
The TFT 47 is disposed opposite to the light shielding layer 42. The color filter 43 is disposed opposite to the pixel electrode 48.
The liquid crystal material 50 is filled in the space between the array substrate and the opposite substrate. Polarizing plates are disposed on both sides of the array substrate and the opposite substrate. The liquid crystal material is used as an optical shutter so that a color picture is displayed.
In recent years, high luminance and low power consumption have been strongly desired for an activate matrix drive type liquid crystal displaying apparatus. Thus, the improvement of the aperture ratio of each pixel has been required. The aperture ratio depends on the black matrix 42 that insulates light from an area free of optical modulation between advancent pixel electrodes. The aperture portion of the black matrix 42 is formed corresponding to the shape of the pixel electrode.
As described above, the light shielding layer (black matrix) 42 is formed on the opposite substrate side as with the color filter 43. However, due to the displacement between the array substrate and the opposite substrate and the difference between the pattern pitch on the array substrate and the pattern pitch of the light shielding layer (black matrix) 42 on the opposite substrate, the size of the opening portion of the light shielding layer (black matrix) 42 should be smaller than the size of the pixel electrode 48.
Thus, the aperture ratio of each pixel deteriorates.
To improve the aperture ratio of pixels, a method of which a black matrix 42 is formed on an array substrate has been proposed. Alternatively, a method of which a pixel electrode 48 of an array substrate is extended to a scanning line and a signal line that surround the pixel electrode 48 has also been proposed. In this method, the scanning line and the signal line are used as a black matrix 42.
In addition to an area between each pixel electrode 48, an outer peripheral area of the panel (outside a display area) should be light-shielded with a light shield layer. In this example, the light shielding layer outside the display area is referred to as a peripheral light shielding layer.
When a light shielding layer is formed on an array substrate, the resistivity should be sufficiently high. Thus, a resin is used as light shield layer material. Because the light shielding ratio of a resin is lower than that of a light shielding material composed of metal, the thickness of light shielding layer composed of a resin should be increased. However, when the thickness of the light shielding layer is increased, the following problem occurs.
Generally, a pixel electrode is patterned with a conductive film formed on the entire surface of the array substrate by the photo process. At this point, a photoresist for patterning the pixel electrode remains in a stage portion on the periphery of the light shielding layer. When the pattern is developed, the photoresist cannot be satisfactorily removed. Thus, the conductive film remains in the stage portion on the periphery of the black matrix.
In particular, when the conductive film remains in the stage portion on the periphery of the light shielding layer, lines in the vicinity of the light shielding layer short-circuit. Thus, display defects, and consequently, product defects, occur.